2.3 Earthquake Hazards and Safety

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Vocabulary

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Liquefaction-process by which a earthquake's violent movement suddenly turns loose soil into liquid mud
Aftershock-an earthquake that occurs after an larger earthquake in the same area
Tsunami- a giant wave caused by an earthquake
Base-isolated building- building mounted on bearings designed to absorb the energy of an earthquake

Outline

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Summary

• January 1995 earthquake
  • Kobe, Japan
  • lasted for 20 seconds
  • caused damage like thousands of buildings collapsed, a lot of crumpled freeways, 130 fires, 5,000 people disappeared
  • most buildings- wood framed, heavy tiled roof

How Earthquakes Cause damage

• severe shaking produced by seismic waves can damage or destroy buildings and bridges, utility poles may fall, and gas and water mains can break
• Local Soil Conditions
  • when seismic waves move from hard, dense rock to loosely packed soil; they transfer their energy to the soil
  • the thicker the layer of soil, the harder the shaking will be
  • a house built on solid rock will not shake as much as a house built on sandy soil
• Liquefaction
  • 1964 earthquake, Anchorage, Alaska
    • cracks opened in the ground (9 meters wide)
    • cracks created by liquefaction
  • liquefaction-likely to happen where soil is moist
  • as ground gives way, buildings sink/pull apart
  • can trigger landslides
• Aftershocks
  • may occur hours, days, or even months later
  • buildings weakened by the earthquake often collapsed during an aftershock
• Tsunamis
  • plate movement causes the ocean floor to rise slightly and push water out of its place
  • in the ocean, the distance between the waves of a tsunami is very long (100-200 kilometers)

Making Buildings Safer

• to reduce earthquake damage:
  • new buildings-made stronger/flexible
  • older buildings- must be changed to withstand stronger quakes
• Choice of location
  • steep slopes- cause landslides
  • filled land- shakes violently
  • avoid buildings near faults
    • the farther a building- less strong shaking will be
• Construction Methods
  • brick/wood framed buildings- collapse if not reinforced
  • plywood sheets- used to strengthen frames of wooden buildings
  • new building on soft ground-anchored to solid rock below soil
  • bridges/highway overpasses- built on supports that go down through soft soil to firm ground
  • fixed-base building- tilts/cracks during earthquakes
  • base-isolated building- upright during earthquakes
  • base-isolation bearings- bend/absorb energy of seismic waves
  • fire/flooding-when gas pipes/water mains break

Protecting Yourself From an Earthquake

• drop, cover, and hold on
• crouch beneath a table/desk
• hold on table/desk so it won't wobble
• if no table/desk is available, crouch against a interior wall and cover your head/neck with hands
• make sure to avoid windows, mirrors, wall hangings, and furniture that may fall
• if outdoors move to open area, and avoid these:
  • vehicles
  • power lines
  • trees
  • buildings
  • and especially brick walls/chimneys(brick kinds)
• you should have an emergency kit
• it should contain these items:
  • water
  • first aid
  • canned food

Diagram

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